1. Field of the Invention
The present invention relates to an injection molding machine, and particularly, to an inline type injection molding machine with a plunger.
2. Description of the Related Art
An inline type injection molding machine performs a molding cycle of plasticizing, measuring, and injecting a molding material by one screw. In the inline type injection molding machine, a molding material is supplied from a material input port formed in a base portion of a barrel to a base portion of a spiral groove formed in the screw, the molding material is plasticized and kneaded while the molding material is fed to the front side of the screw with the rotation of the screw, and the molding material is metered at the front side of the screw. Subsequently, a mold is closed, and the molding material is injected into the mold as the screw moves forward, thereby obtaining a molded product.
Hitherto, even in a case where the inline type injection molding machine molds a molding material such as liquid silicon having very low viscosity or does not need to perform a plasticizing or kneading operation, the molding material is injected from the material input port formed in the base portion of the barrel to an inner diameter portion of the barrel corresponding to the base portion of the screw, and the screw moves backward in a rotation state, so that the molding material is metered at the front side of the screw.
However, in the case of a molding material having very low viscosity which does not need the plasticizing and kneading operations or substantially does not need the plasticizing and kneading operations, a problem arises in that the material is degraded due to the shearing operation performed by the screw. Further, in the case of a molding material which needs slight shearing and kneading operations or the case of a screw with a flight, there is a case in which the molding material is sheared and kneaded too much.
Further, since a feeding force is needed due to the spiral structure of the flight for feeding the molding material to the front side of the screw regardless of the unnecessary kneading operation, an expensive screw with a spiral groove is needed.
Although a preplasticating type injection molding machine is also known, even this injection molding machine includes a device that plasticizes and kneads a molding material by a screw and feeds the molding material toward a nozzle as in the inline type injection molding machine. As a result, there are problems in that the molding material is sheared and degraded and the expensive plasticizing and kneading device is needed (JP-A 2006-334974 and JP-A 8-80549).